1. Field of the Invention
The present invention relates to a thin film transistor having an etching protection film and manufacturing method thereof.
2. Description of the Related Art
Unexamined Japanese Patent Application KOKAI Publication H 5-67786 discloses a structure as a thin film transistor used as a switching element of an active matrix liquid crystal display device. The thin film transistor includes a gate electrode formed on an upper surface of an insulating substrate, a gate insulating film formed on the upper surface of the insulating film including the gate electrode, an intrinsic amorphous silicon semiconductor thin film formed on an upper surface of the gate insulating film on the gate electrode, a channel protection film formed on a central portion of an upper surface of the semiconductor thin film, n-type amorphous silicon ohmic contact layers formed on both sides of an upper surface of the channel protection film and an upper surface of the semiconductor thin film on its both sides, and a source and drain electrode formed on an upper surface of each ohmic contact layer.
In recent years, the use of a metal oxide semiconductor such as a zinc oxide (ZnO) instead of amorphous silicon has been considered in view of higher mobility. The manufacturing method of the thin film transistor using the metal oxide semiconductor can be considered as follows. For example, an intrinsic ZnO semiconductor thin film forming layer is film-formed on a gate insulating film, and a silicon nitride channel protection film is pattern formed on the semiconductor thin film forming layer. Next, an n-type ZnO ohmic layer forming layer is film-formed on an upper surface of the semiconductor thin film forming layer including the channel protection film, and the ohmic contact layer forming layer and the semiconductor thin film forming layer are continuously pattern formed to form an ohmic contact layer and a semiconductor thin film on a device area. Sequentially, a source and drain electrode is pattern formed on an upper surface of each ohmic contact layer.
However, in the aforementioned manufacturing method, there is a problem in which the zinc oxide easily dissolves in both acid and alkali and its etching resistance is extremely low, thereby causing relatively large side etching in the ZnO semiconductor thin film and the ohmic contact layer formed on the device area in post-process to worsen machining accuracy.